This looks good, thank you. Sorry for asking basic questions, but I have added to my mytheme.theme changed the 'name' appropriately, as well as the 'field_something', cleared the drupal caches, but still nothing. Is there any step I'm missing?

The field is a part of a page / content type that is being displayed, if that is what you mean.

When I display content which is not translated, the original (English) is displayed. That is actually what I want - what I don't want is all of the translated parts of the page, like menus, etc. to change to English as well. I would like to display the fallback English language of the node, while displaying the rest of the page (menus, etc.) in the local language, so that when I leave the non-translated node's page and move to a translated node, the browser will still remember my local language choice and display that instead of English.

No answers? :-(

Sounds good. I tried adding the code above to mytheme.theme, cleared the cache and rebuilt, but there's no change. Anything else I might have to do?

Right, so there's really no inbuilt way to do this - at least I know that for sure now :) I'm not a module developer, so, can this be somehow done on the theme level (like in mytheme.theme maybe)?

I don't use a view for this. I am using the out-of-the-box search that you get on a fresh install of D8. The only way I found to modify the behavior of the search is either through Configuration > Search Pages or via twig templates.

So, if I'm not a programmer, I have to do this manually, there's no clickable interface to do this, right?

I thought that if I would be able to do this, if the paths could stay the same regardless the language, all the links on the website could also be the same regardless the language. Pitty, that would make administration somewhat easier in our environment. I'll try to manually adjust the paths, since they are configured to be translatable.